I have a few favorites, so I will put them into categories.
The most outrageous submarine would have to be the French Surcouf class submarine. It was essentially a submerged destroyer with double eight inch guns not to mention the 12 torpedo tubes. For how much work and effort was put into making this monster it was lost in February 1942 in a collision with an American freighter.
The most ingenious submarine would be the Japanese the I 300 class submarines. It was designed to hold four aircraft that would be launched from a ramp. They were designed to attack the Panama Canal but the attack never happened.
For modern submarines-
The most economic submarine would be the German Type 209 submarine. Exported to a myriad of nations, it is cheap, highly effective for defense, and an all around solid vessel.
The best attack submarine I think would be the Akula...if the funding existed to keep the repairs up. With it immense diving limit and silence along with its innovative anti-submarine missile I think it would give a good fight against any opponent. However, due to the current state of the Russian navy I don't think many are operational. So for offensive purposes I would have to give my vote to the Seawolf.
Now for the submarine that I just happen to really like for no specific reason. And many specific in fact. THE TYPHOON!!!
Alice came to a fork in the road. "Which road do I take?" she asked.
"Where do you want to go?" responded the Cheshire cat.
"I don't know," Alice answered.
"Then," said the cat, "it doesn't matter."